Project Summary Some cutaneous malignant melanoma (CMM) patients experience a sudden and rapid decline in their night vision often accompanied by photophobia and a sensation of shimmering light. These symptoms are a hallmark of a paraneoplastic autoimmune syndrome known as melanoma-associated retinopathy (MAR), which is clinically diagnosed by a reduced b-wave on the electroretinogram. We and others have identified the TRPM1 cation channel as the autoantigen. TRPM1 channels are expressed in melanocytes and retinal ON- bipolar cells, thus autoantibodies against TRPM1 block ON bipolar cell responses. A tumor suppressor microRNA, miR-211, is encoded within the 6th intron of TRPM1 and co-transcribed with TRPM1. Full-length TRPM1 and miR-211 are down regulated in metastatic disease, yet this is when TRPM1 autoantibodies are typically detected. We propose that the autoantibodies are generated against truncated, antigenic TRPM1 polypeptides encoded by abnormal TRPM1 mRNA splice variants, associated with reduced expression of miR-211.. The overall rationale of the proposed studies is that the occurrence of TRPM1 autoantibodies is more widespread in CMM patients than suggested by the incidence of clinically diagnosed MAR, and that the increased use of targeted and immuno therapies may heighten the risk of MAR. The proposed project aims to determine the incidence of TRPM1 autoantibodies and sub-clinical MAR among CMM patients and whether it varies according to treatment. Further, we aim to identify which TRPM1 mRNA splice variants give rise to immunoreactive TRPM1 polypeptides and test our hypothesis that these polypeptides are present in CMM specimens from patients with TRPM1 autoantibodies and sub-clinical MAR, and are associated with a down- regulation of miR-211. Thus, we will generate new insights into the cellular mechanisms underlying MAR, which may be further relevant to paraneoplastic autoimmune diseases in general. Potential applications of this research include the development of a prognostic/diagnostic test that can be used in the clinic for assessing CMM patients' risk of MAR and tumor metastasis.